1. Products and Versions Concerned
(1) The C compiler package--M3T-NC308WA--for the M32C series*1
V.5.40 Release 00 through V.5.41 Release 01
(2) The C compiler package--M3T-NC30WA--for the M16C series**
V.5.40 Release 00 through V.5.43 Release 00
*Generic name of the M32C/80, and M16C/80 series.
**Generic name of the M16C/60, /30, /20, /10, /Tiny and R8C/Tiny series.
2. Problem
When arguments are passed to functions via the stack, they may
incorrectly be referenced, or the programs containing such functions
may run away.
3. Conditions
This problem occurs if the following conditions are all satisfied:
(1) Compile option -OR or -OR_MAX (-ORM) is selected.
(2) Compile option -Ono_asmopt (-ONA) is not selected.
(3) In a file, a function to which its argument is passed via the stack
(function A) is called from other two or more functions (for example,
functions B and C below).
(4) At least either function B or C satisfies any of the following
conditions (under any of these conditions, the "exitd" instruction
is generated, which terminates the function):
- The function takes an argument passed via the stack.
- The function is using an auto variable (corresponding
the temporary area generated by the compiler).
- The -genter option is used at compilation.
(5) After the program has returned from function A, no code for
adjusting the stack exists in it until an exitd instruction
is executed.
(6) After the argument of function A has been saved, the same code
exists in functions B and C until function A is called by a jsr
instruction.
(7) Function A takes an argument passed via the stack.
Example:
----------------------------------------------------
void func1( void ) // Function B
{
. . . . . . . . . . .
comm_func ( int i, int *p, int *q ); // Function A called
. . . . . . . . . . .
}
void func2 ( void ) // Function C
{
. . . . . . . . . . .
comm_func ( int i, int *p, int *q ); // Function A called
. . . . . . . . . . .
}
----------------------------------------------------
Explanations:
In the above example, the code shown below is generated at the places
where function A is called from functions B and C.
----------------------------------------------------
. . . . . . . . . . .
push.w _q
push.w _p
mov.w _i,R1 // D
jsr $comm_func // E
exitd
. . . . . . . . . . .
----------------------------------------------------
Since compile option -OR or -OR_MAX is selected under Condition (1),
it converts the lines D and E above to the common function _aopt_xxx
as shown below.
As a result, the arguments in the lines F and G below that are saved on
the stack will be stored at an address to which the addresses consumed
by the stack to call _aopt_xxx are accumulated.
On the other hand, because the code generated from $comm_func remains
the same as before the lines D and E are converted to _aopt_xxx, the code
will reference an address different from the one where the arguments of
function A has been saved.
----------------------------------------------------
. . . . . . . . . . .
push.w _q // F
push.w _p // G
jsr _aopt_xxx
exitd
. . . . . . . . . . .
_aopt_xxx:
mov.w _i,R1
jsr $comm_func
exitd
----------------------------------------------------
4. Workarounds
This problem can be avoided in any of the following ways:
(1) If function A is called indirectly, select the -ONA compile
option.
(2) If function A is a special page function, select the -ONA option
or place a dummy asm function immediately after a call to
function A, which is shown in Example below.
(3) If function A does not meet the assumptions in (1) and (2) above,
select the -ONA or -OSA option, or place a dummy asm function
the same manner as described in (2)
Example:
----------------------------------------------------
void func1( void )
{
. . . . . . . . . . .
comm_func ( int i, int *p, int *q );
asm(); // asm function placed
. . . . . . . . . . .
}
----------------------------------------------------
5. Schedule of Fixing the Problem
We plan to fix this problem in the next release of the products.
